improve contact lens visual acuity and peripheral vision are often stronger than glasses and can prescribed to correct: Myopia (overview of refractive errors) hyperopia (overview of refractive errors) astigmatism (overview of refractive errors) anisometropia (overview of refractive errors) Aniseikonia (a difference in image size) aphakia (aphakia) (after cataract surgery keratoconus conically shaped corneal keratoconus) For the correction of myopia and hyperopia soft or hard contact lenses are used. Toric soft contact lenses (various preformed bends on the front of the lens have) or hard contact lenses can correct an astigmatism significant in many cases sufficient, but must be adjusted by an expert. Contact lenses are also used to correct presbyopia. A correction possibility which is referred to as monovision, is to adjust the non-dominant eye for near vision (reading) and the dominant eye for distance vision. Hard and soft bifocal and multifocal contact lenses also can be adapted successfully. However, this is very time consuming because a precise adjustment is crucial. Neither hard nor soft contact lenses protect the eyes from blunt or sharp injury, as do lenses. Care and complications instructions for handling the lenses and hygiene must be strictly adhered to. Poor contact lens hygiene can lead to an infection of the cornea or a persistent inflammation. Contact lenses occasionally cause painless superficial corneal changes. Contact lenses can be painful if the corneal epithelium is eroded (corneal erosions and foreign bodies), the eye is red and the corneal stained by fluorescein. the lenses fit poorly (z. B. too tight, too loose, ill-centered). is too little moisture present, so that the lens can slide on the cornea. the lenses (eg. as O2 poor, smoky, windy) are carried in a non-ideal environment. a lens is not properly inserted or removed. a small foreign particles (eg. as soot, dust) is trapped between the lens and the cornea. the lenses are worn for a long time (over Wear syndrome). When Over Wear syndrome spontaneous healing within a day or a few days can be done, provided that the lenses are not worn. In some cases, is an active treatment is required (eg. B. topical antibiotic eye drops or ointments). The extension of the eye with mydriatic drops can alleviate photophobia. The effect of mydriatic based on a temporary paralysis of the iris and Ziliarkörpermuskeln (the movement of the inflamed muscles causing pain). When Over Wear syndrome or persistent pain after lens removal, an ophthalmologist should be consulted before the lenses are worn again. Risk factors for associated with contact lens corneal infection (keratitis) include the following factors: poor contact lens hygiene Nocturnal or pronounced wearing the lenses using tap water to clean eyes with a compromised surface (such as drought, reduced corneal sensitivity.) Infections must be treated quickly ophthalmologically. Corneal ulcer A corneal ulcer, which is a potential visusgefährdende infection of the cornea is suspected when a contact lens wearers intense eye pain has (both foreign body sensation and pain), redness, photophobia, and lacrimation (corneal ulcer). The use of contact lenses increases the risk of corneal ulcers. The risk increases by about 15 times when contact lenses are worn overnight. Corneal ulcers can be caused by bacteria, viruses, fungi or amoebae. A slit lamp examination with fluorescein staining leads to the diagnosis. A defect of the corneal epithelium (which by fluorescein stain) and a corneal infiltrate (collection of leukocytes in the corneal stroma) are present. Sometimes the cornea defect is so extensive and dense that it can be seen with a magnifying held by the hand or the naked eye as a white spot in the cornea. In the event a microbiological examination of cultures and smears of Hornhautinfiltrats, the contact lens and the contact lens storage case is indicated. The use of contact lenses is set. Antibiotic eye drops are given empirically for possible bacterial infection. The initial treatment makes use of a broad spectrum antibiotic, said antibiotic fluoroquinolone eye drops are used around the clock every 15 to 60 minutes until after 24-72 h, the intervals may be extended gradually. If the ulcer is large or deep or located near the visual axis, more antibiotic eye drops such as cefazolin, vancomycin or concentrated tobramycin are used. The antibiotic may be changed or discontinued later based on the results of the culture. Too careless treated cases may poorly or not respond to therapy and have a severe vision loss result. Hard contact lenses A rigid lens may be more correct the natural shape of the cornea into a new, better refracting surface as a soft lens and therefore is more likely to be a consistent improvement of refraction in people who have astigmatism or irregular corneal surface. The older hard contact lenses made of polymethyl methacrylate have been replaced by gas-permeable contact lenses made of fluorocarbon with polymethyl methacrylate addition. Gas permeable contact lenses with their diameter from 6.5 to 10 mm cover a portion of the cornea and float on the tear film. Hard contact lenses can improve visual acuity in people with myopia, hyperopia and astigmatism. Rigid contact lenses can also correct corneal irregularities such as keratoconus. In most cases, seeing patients with keratoconus with rigid contact lenses better than with glasses. Gas permeable contact lenses can be manufactured so that they fit exactly to the eye. For a good comfort they require insertion time of typically 4-7 days. During this time, the contact lens wearing time is increased daily by the hour. It is important that pain should occur at any time. Pain is a sign of poorly adapted contact lenses or corneal irritation. After removal of hard contact lenses contact lens wearers see mostly temporary (<2 h) despite its own worn glasses blurred (Spectacle blur). Soft hydrophilic contact lenses Soft contact lenses made from poly-2-hydroxyethylmethacrylate and other flexible plastics (such as silicone-hydrogel), as well as 30-79% water. With a diameter of 13 to 15 mm to cover the entire cornea. Soft contact lenses are often daily (disposable lenses), every 2 weeks or replaced monthly. Soft contact lenses can improve with myopia and hyperopia visual acuity in humans. As to adapt soft contact lenses to the existing corneal curvature, they can compensate for only a minimal astigmatism. A stronger astigmatism can be corrected with toric special lenses that have different pre-formed curvatures on the front of the lens. The heavier lower portion of toric lenses reduces the lens rotation and thus (then as dressing or therapeutic contact lenses hereinafter) receives its alignment Soft contact lenses are also used to treat Hornhautabrasio, recurrent erosions or other corneal diseases prescribed. With a bandage contact lens for prophylactic treatment with antibiotic-containing eye drops (z. B. fluoroquinolone 4 times a day) is recommended. Soft contact lenses extended wear are very practical especially in aphakia after cataract surgery. However, the patient must be examined regularly by an ophthalmologist. The patient should be cleaned once a week the lens. Soft contact lenses are larger and therefore do not fall as easily as hard contact lenses out of the eye. Foreign bodies can not easily settle among them. Since they are immediately perceived as pleasant, the insertion time of soft contact lenses is short. Soft contact lenses frequently lead to corneal infections as a gas-permeable contact lenses, especially when soft contact lenses are worn overnight. Dried soft contact lenses are brittle and break easily. In order to retain their shape and flexibility, they absorb (in relation to their water content) of moisture from the tear film. Therefore, patients come with dry eyes usually better with contact lenses cope that have a low water content.